MORPHOLOGY AND PROPERTIES OF POLYCAPROLACTONE-POLY(DIMETHYL SILOXANE)-POLYCAPROLACTONE TRIBLOCK COPOLYMERS

The molecular structure, crystallization, solid-state morphology, thermal properties, and phase behavior of two copolymers consisting of a poly (dimethylsiloxane) (PDMS) mid-block coupled to polycaprolactone (PCL) end-blocks were investigated. Both copolymers (which differ only in the molecular lengths of the PCL end-blocks) were found to be lamellar systems, whose core consists of PCL chains having the same crystal structure as PCL homopolymer, and whose amorphous interlayers contain the PDMS blocks and the PCL noncrystalline segments. From x-ray and electron-microscopy results, it is expected that the PCL blocks may be folded once in the longer copolymer and not at all in the shorter. As a result of their differing PCL lengths, the former crystallizes as regular PCL spherulites (at a growth rate reduced with respect to PCL homopolymer), whereas the latter yields only defective, immature axialites of low overall crystallinity. Electron diffraction showed that these spherulites grow preferentially along the b crystallographic axis and that the PCL crystalline stems are arranged perpendicularly to their lamellae.